Traditional security systems are generally designed for a specific use, and consequently are not adapted to perform a multiplicity of functions. For example, security systems have been used as intrusion sensing units to secure a building or other enclosure by locating intrusion sensors at doors, windows, and other secured openings. These intrusion sensors may employ infared, microwave, and ultrasonic motion detectors, or photoelectric beams which are broken when an intrusion occurs. Such systems are generally static systems which are wired to a building power supply, and consequently these systems are not adaptable to other uses.
Known security systems also include alarm systems which are specifically designed to protect personal property which may be easily moved and concealed. These systems, which are widely used in department stores and similar merchandising institutions, generally employ fixed receiver units located at specific points in the store. These receiver units are responsive to special tags or other removable transmitting devices which may attached to the personal property. If these transponders are not removed from the property, an alarm will be triggered as the property is moved past a gate equipped with a sensing receiver unit.
Finally, traditional security systems include a number of personal alarm systems which generally include at least a portable transmitter. One category of personal alarm system is designed to operate in the audio range and provide a loud noise to attract the attention of people in the vicinity who might provide aid to the party triggering the alarm. Another type of personal alarm system is the silent alarm which provides no audible signal in the vicinity of the alarm transmitter. Systems of this type generally employ radio signals which are picked up by receivers installed in a protected area, and these systems transmit some type of identification code unique to the transmitter.
In an attempt to provide a security system which is more versatile than the traditional security systems, a multi-function security system has recently been devised which is based upon ultrasonic energy transmission. The major units of this system are primarily interconnected by ultrasonic sound waves and thus require no installation wire. Such a system, as disclosed in U.S. Pat. No. 4,367,458 to Kenneth R. Hackett, utilizes a plurality of transponders which can be interrogated from a central data unit for reporting back operative or inoperative condition alarm situations in the vicinity of local transponders. Although multiple functions may be provided by the system by initial programming and by key control operation of the system once it is installed, this ultrasonic system is still primarily a static system which cannot be adapted for a plurality of different uses. Additionally, although this known prior art system employs transponders capable of transmission and reception of a plurality of different ultrasonic frequencies, the frequencies are transmitted sequentially and not simultaneously, and all of the transmitted frequencies are in the non-audible range. Thus, the system is not adapted to provide an audible signal.